No - if you are doing macro shots you already get a pretty damn shallow depth of field and stopping down you can get more. Some examples: (Sorry, I only have the 100mm 2.8, not the 50mm 2.5 although that's on my list as a possible replacement for the 50mm 1.8 II)

Canon EOS 500DCanon EF 100mm 2.8L Macro IS USMF2.8ISO 1001/500 secOnly the eye is sharp and the rest of that little guy is out of focus.

Canon EOS 500DCanon EF 100mm 2.8L Macro IS USMF5.6ISO 1001/200 secHere you can see it's much sharper - but still the depth of field is shallow enough to get a pretty blurred background.

Canon EOS 500DCanon EF 100mm 2.8L Macro IS USMCanon Speedlite 580EX II (master)Nissin Speedlite Di466 (slave)F20ISO 4001/200 secThe depth of field is getting pretty usable for macro work. But still the depth is not really big - at F20! Half the problem with the 50mm though. You are just loosing a lot of light.

And a last one...Canon EOS 33vCanon EF 100mm 2.8L Macro IS USM F22Agfa APX 1001/5 sec No, I don't smoke, but the cigarette is almost completely in focus.

So the point of macro lenses is to get small things as big as possible and most of the time those lenses are pretty sharp. Most "portrait" lenses let more light through. 50mm 2.5 --> macro50mm 1.8, 1.4, 1.2, 1.0 --> no macro100mm 2.8 --> macro100mm 2.0 --> no macro